That LH pulsatility is disrupted and that mental and physical performances are degraded abruptly at a particular threshold of energy availability; that this threshold corresponds to a level of energy availability at which the hormonal regualtion of metabolism alters the mobilization and utilization of stroed metabolic fuels and reduces resting metabolic rate to compensate for energy deficiency; that this level of energy availability is higher in women than in men, making women more susceptible than men to the harmful effects of low energy availability.